Re: [PATCH v2] arm64: compat: Implement misalignment fixups for multiword loads
On Mon, Sep 05, 2022 at 12:04:47PM +0200, Ard Biesheuvel wrote: > On Wed, 31 Aug 2022 at 19:07, Catalin Marinas wrote: > > On Fri, Jul 01, 2022 at 03:53:22PM +0200, Ard Biesheuvel wrote: > > > +config COMPAT_ALIGNMENT_FIXUPS > > > + bool "Fix up misaligned multi-word loads and stores in user space" > > > + default y > > > > For consistency with ARMV8_DEPRECATED, I think we should keep this as > > default n. > > Fair enough. I take it you can fix this up while applying? Yes. -- Catalin
Re: [PATCH v2] arm64: compat: Implement misalignment fixups for multiword loads
On Wed, 31 Aug 2022 at 19:07, Catalin Marinas wrote: > > On Fri, Jul 01, 2022 at 03:53:22PM +0200, Ard Biesheuvel wrote: > > The 32-bit ARM kernel implements fixups on behalf of user space when > > using LDM/STM or LDRD/STRD instructions on addresses that are not 32-bit > > aligned. This is not something that is supported by the architecture, > > but was done anyway to increase compatibility with user space software, > > which mostly targeted x86 at the time and did not care about aligned > > accesses. > > > > This feature is one of the remaining impediments to being able to switch > > to 64-bit kernels on 64-bit capable hardware running 32-bit user space, > > soDocumentation/x86/boot.rst let's implement it for the arm64 compat layer > > as well. > > > > Note that the intent is to implement the exact same handling of > > misaligned multi-word loads and stores as the 32-bit kernel does, > > including what appears to be missing support for user space programs > > that rely on SETEND to switch to a different byte order and back. Also, > > like the 32-bit ARM version, we rely on the faulting address reported by > > the CPU to infer the memory address, instead of decoding the instruction > > fully to obtain this information. > > > > This implementation is taken from the 32-bit ARM tree, with all pieces > > removed that deal with instructions other than LDRD/STRD and LDM/STM, or > > that deal with alignment exceptions taken in kernel mode. > > > > Cc: debian-arm@lists.debian.org > > Cc: Vagrant Cascadian > > Cc: Riku Voipio > > Cc: Steve McIntyre > > Signed-off-by: Ard Biesheuvel > > --- > > Note to cc'ees: if this is something you would like to see merged, > > please indicate so. This stuff is unlikely to get in if there are no > > users. > > > > v2: - drop some obsolete comments > > - emit a perf alignment-fault event for every handled instruction > > - use arm64_skip_faulting_instruction() to get the correct behavior > > wrt IT state and single step > > - use types with correct endianness annotation (instructions are > > always little endian on v7/v8+) > > It looks like that's a fairly popular request from people running 32-bit > user on AArch64 kernels, so happy to queue it for 6.1 (if it still > applies cleanly). I'm not too keen on code duplication but it's a lot > more hassle to create a common decoding/emulation library to share with > arch/arm, especially as such code is not going to change in the future. > > > +config COMPAT_ALIGNMENT_FIXUPS > > + bool "Fix up misaligned multi-word loads and stores in user space" > > + default y > > For consistency with ARMV8_DEPRECATED, I think we should keep this as > default n. > Fair enough. I take it you can fix this up while applying?
Re: abel.d.o + gcc-12.x
On 2022-09-05 08:53 +0200, Mathieu Malaterre wrote: > Dear Debian arm porters, > > I have two requests: > > - Could someone please check the status of abel.d.o ? (*) It does not not boot any more after a kernel upgrade. This happened whilst I was on holiday so it's taken a while to get to it. It is now on my desk being looked at. > - One of gcc dev asked me to verify the status of a bug in gcc-12.x > branch. Are there any pre-build version of GCC 12.x package for > Debian/arm ? (**) Yes: 12.2.0 is in the archive: https://tracker.debian.org/pkg/gcc-12 https://buildd.debian.org/status/package.php?p=gcc-12 https://deb.debian.org/debian/pool/main/g/gcc-12/ Wookey -- Principal hats: Debian, Wookware, ARM http://wookware.org/ signature.asc Description: PGP signature
Re: abel.d.o + gcc-12.x
On Mon, Sep 5, 2022 at 2:54 AM Mathieu Malaterre wrote: > > Dear Debian arm porters, > > I have two requests: > > - Could someone please check the status of abel.d.o ? (*) > - One of gcc dev asked me to verify the status of a bug in gcc-12.x > branch. Are there any pre-build version of GCC 12.x package for > Debian/arm ? (**) > > Thanks much, > > (*) I cannot post to 'ad...@db.debian.org', I get a '550 host > 209.85.221.48 is listed in safe.dnsbl.sorbs.net (127.0.0.6);' > (**) https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1018953 >From the GCC bug report: > I can trigger an assertion in highway unit test suite > on armhf when using -O2 (does not happen at -O0). > > Symptoms: > > % tests/mul_test > "--gtest_filter=HwyMulTestGroup/HwyMulTest.TestAllMulAdd/Emu128" > "--gtest_also_run_disabled_tests" > Running main() from ./googletest/src/gtest_main.cc We encountered a similar bug under GCC 12. We are also a C++ project. Things were Ok at -O1, but segfaulted at -O2 or higher. We found GCC was removing live code. -fsanitize=unreachable helped uncover the problem. [1] We needed to add -fno-devirtualize to our CXXFLAGS. It is just a workaround at the moment. We hope the GCC flks will get it sorted out soon. Jeff [1] https://github.com/weidai11/cryptopp/issues/1141
Re: abel.d.o + gcc-12.x
Hi Adrian, On Mon, Sep 5, 2022 at 9:11 AM John Paul Adrian Glaubitz wrote: > > > > > On Sep 5, 2022, at 8:54 AM, Mathieu Malaterre wrote: > > > > I have two requests: > > > > - Could someone please check the status of abel.d.o ? (*) > > - One of gcc dev asked me to verify the status of a bug in gcc-12.x > > branch. Are there any pre-build version of GCC 12.x package for > > Debian/arm ? (**) > > If you have a Debian DSA account, you can just create a armel schroot session > for sid. > > In sid, gcc-12 is now the default compiler. I should have said: "I need a GCC 12.3" compiler (on amdahl.d.o).
Re: abel.d.o + gcc-12.x
> On Sep 5, 2022, at 8:54 AM, Mathieu Malaterre wrote: > > I have two requests: > > - Could someone please check the status of abel.d.o ? (*) > - One of gcc dev asked me to verify the status of a bug in gcc-12.x > branch. Are there any pre-build version of GCC 12.x package for > Debian/arm ? (**) If you have a Debian DSA account, you can just create a armel schroot session for sid. In sid, gcc-12 is now the default compiler. Adrian
